The logic of the `revng ptml` command was too tightly coupled with the
parsing of the xml. Overhaul the structure of the ptml code and split it
in two locations:
* `revng.ptml`: this module contains functions that allow easy
manipulation of PTML, both for printing it and for obtaining the split
metadata/text version.
* `revng.internal.cli._commands.ptml`: this implements the actual `revng
ptml` command. This leverages the new logic in the `revng.ptml` module
while maintaining the same functionality.
At the moment this pipe is broken, because it claims to be producing
artifacts with function rank, while it only produces types.
This pipe should be extended and turned into a pipe that generates
the whole Clift module including functions from LLVM IR, and not just
types.
We should add an input LLVMContainer, and the run() method should first
import types, and then create the functions and their bodies.
For the time being the Pipe is removed from the pipeline.
The previous conversion from LLVM to MLIR was translating plain LLVM IR
to LLVM MLIR Dialect, as a preliminary step for further conversion from
LLVM MLIR Dialect to Clift.
This is not how things are expected to work anymore, so the old code is
now dead and can be removed.